Re: Multi Valued Interface Models?
Date: 12 Feb 2006 14:34:27 -0800
paul c wrote:
> David Cressey wrote:
> > "dawn" <dawnwolthuis_at_gmail.com> wrote in message
> >>OK, no, my argument is that it is not possible to employ the RM as the
> >>data model for a general user interface. Surely you can use the RM to
> >>persist data that makes its way to a UI, but you cannot use the RM as
> >>the data model of the interface to the user. You need an understanding
> >>of what a data model is (e.g. from my blog entry The Naked Model).
> >>Then separate yourself from thinking about the data model for the
> >>database (that is the model of the interface to the database) and focus
> >>on the data model of the interface to the user. It simply is not
> >>possible for the RM to be the data model for that interface.
> > Not possible, or not useful?
> > It seems to me that for every unnormalized schema of relations, there exists
> > an normalized schema that can convey the same information. ...
> Many, I'd guess.
A logical model of the data is developed in a programming language that implements a data model. If you take SQL or Tutorial-D or any other implementation(ish) of the RM, is there code you can write using only those languages that would give you the data model for a UI (an arbitrary one)? Not unless the language is extended to permit multivalued attributes (and not just relation-valued attributes or you miss possible ordering of such).
> > I think that's what Codd said.
> > It seems to me that for any possible set of information requirments, there
> > exists a (possibly unnormalized) schema of relations that can convey that
> > information.
There are schema from which you can use a 3GL, for example, to handle an arbitrary UI, but you cannot use the RM as the model for the language which handles the UI.
> > I know you claimed to the contrary regarding a model to back a
> > web page, but I have yet to be convinced of that.
While it is certainly the case that you can have data in an RM schema and then work with that data in a UI, you cannot use an RM-language-implementation as the exclusive means of working with a UI. That is, you cannot use the RM as the data model for the UI (not talking about the data model for the database). I'm working on my next blog entry to try to see if I can state this more clearly. Cheers! --dawn Received on Sun Feb 12 2006 - 23:34:27 CET